1. Field of the Invention
The present invention relates to a system and method for measuring product flow in an agricultural implement, and, more particularly, to such a system and method used with an agricultural seeding implement.
2. Description of the Related Art
Generally, seeding implements are towed behind a tractor or other work vehicle via a hitch assembly secured to a rigid frame of a planter or seeder. These seeding implements typically include one or more ground engaging tools or openers that form a seed trench for seed deposition into the soil. The openers are used to break the soil to enable seed deposition. After the seeds are deposited, each opener is followed by a packer wheel that packs the soil on top of the deposited seeds.
Air seeders are commonly towed by a traction unit, e.g., an agricultural tractor, to apply a material such as seed, fertilizer and/or herbicide to a field. An air seeder has as a primary component a wheeled air cart which includes one or more frame-mounted tanks for holding material. In the case of multiple tanks, the tanks can be separate tanks, or a single tank with internal compartments. The air cart is typically towed in combination with a tilling implement, such as an air drill, one behind the other, to place the seed and fertilizer under the surface of the soil. Air seeders generally include a metering system for dispensing material from the tanks and a pneumatic distribution system for delivering the material from the tanks to the soil. A centrifugal fan provides at least one airstream which flows through the pneumatic distribution system. Material is first introduced to the air stream by the metering system at a primary distribution manifold located below the metering system. The tanks of the air seeders are formed with bottom surfaces that slope downward at an angle of repose for the granular material toward the metering system. Gravity, in combination with the vibrations and movement of the air seeder, act to move the granular material from the perimeter of the tank toward the metering system located at the center of the tank. Material is carried by the air stream through distribution lines to a series of secondary distribution manifolds, which in turn distribute the material through distribution lines to seed boots mounted behind ground openers on the tilling implement so that the product may be evenly delivered to the ground which is tilled by the tilling implement.
To ensure that a desired quantity of product is delivered, a calibration procedure may be performed to calibrate rotation of meter rollers within the metering system to a mass flow rate of product to the openers. Some calibration procedures involve user intervention throughout the process. For example, a user may attach a bag to the metering system to collect expelled product. The user may then instruct the metering system to rotate the meter rollers through a desired number of rotations (e.g., 50 100, 150, 200, etc.). Next, the user may weigh the collected product and enter the weight into a user interface. A controller may then automatically compute a calibration that associates product mass flow rate with rotation of the meter rollers. Such user intervention may be time consuming, and may result in inaccurate calibrations, thereby causing too much or too little product to be delivered.
Current product delivery systems assume that the meter roller has been properly calibrated and remains operating properly throughout usage. Air seeders currently do not provide feedback on the product mass flow rate of the product being conveyed. With a technology shift toward variable-rate and independent control of product flow rates, knowledge of the actual flow within the air seeder will be important to properly controlling the air delivery system. Existing methods for pressure-based mass flow rate determination are either purely empirical, or rely on the flow being fully accelerated and the air velocity being well above a minimum conveying velocity of the product being conveyed. Neither of these conditions are amenable to application on an air cart/drill.
For example, U.S. Pat. No. 8,746,158 (which is assigned to the assignee of the present invention) discloses a pressure based mass flow rate system and method using empirical data. A controller receives pressure sensor signals to determine a pressure drop across a known length of pipe, and compares the pressure drop with data from an empirical pressure database.
What is needed in the art is a faster and more accurate system and method for determining the mass flow rate of a product being conveyed in an air seeder, particularly in regions of undeveloped air flow within the product delivery system.